Food allergies in horses are often suspected but in reality is the high level of suspicion justified? Here we uncover the truth about food allergies including what they are, how likely it is that your horse may have one and why current tests used to diagnose them shouldn’t be relied upon.
What is a food allergy?
A food allergy is caused by the body’s immune system mistaking a specific type of protein as harmful. In most cases the immune system produces specific antibodies to ‘fight off’ the offending allergen. This results in the production of a number of chemicals (including histamine) which causes inflammation. In humans, symptoms usually develop within minutes of eating and commonly include urticaria/ hives, swelling, sickness, diarrhea, stomach pain, blocked or runny nose and wheezing. It only takes very small amounts of the given protein to cause a reaction which is why statements such as ‘may contain traces of nuts’ are so important on human food labels.
Do equine food allergies really exist?
Yes, although they are very rare. Food allergies are thought to affect just 1-2% of adults in the UK and the true prevalence in horses is likely to be even lower. When they do occur, a specific cereal derived protein is the most common culprit.
Food allergies only occur in response to a specific type of protein which means it simply isn’t possible for horses to be allergic to sugar or oil (oil does not contain any protein). In fact, glucose is the main source of energy used by the brain and if insufficient levels are provided by the diet, the body will convert other nutrients in order to meet demand.
Unfortunately both serum allergy tests (blood tests) and intradermal skin testing or ‘skin prick tests’ are unreliable in horses. In a study by Dupont et al (2014), serum allergy tests were completed in 17 ponies on two separate occasions. Whilst 35% of ponies tested positive for allergies on both occasions, no pony reacted to all of the same allergens in both tests. Furthermore, consuming the feeds they were reportedly allergic to 14 days did not cause any clinical signs of an allergic reaction or any increase in inflammatory blood markers. Intradermal skin testing, which involves injecting a series of potential allergens under the skin to see if they elicit a response, can often result in false positives. If a genuine feed allergy is suspected, an elimination diet is therefore the best course of action.
An elimination diet involves removing all feed and supplements (except forage) from the horse's diet for a period of 4-6 weeks. If the ‘reaction’ (hives, itching etc.) disappears, the immune system is then challenged by introducing individual feeds/ ingredients one at a time to see if it returns. Although you may not be keen on the idea of intentionally inducing a reaction, this is an essential step as it helps to rule out the possibility that any seemingly positive effect of removing the feed was purely a coincidence (which is often the case!).
Allergy vs. intolerance
Unlike allergies, food intolerances are not caused by the immune system and are never life threatening. Although more common (in people), intolerances are very difficult to diagnose and whilst many people suspect they have a food intolerance, the true prevalence is unknown. Symptoms generally take several hours or sometimes days to develop and in most cases, it takes larger quantities of the given food/ ingredient to cause a reaction. Food intolerances in horses are also thought to be extremely rare but if suspected, an elimination diet is again the best course of action.
For more advice on feed allergies contact the SPILLERS Care-Line